java使用正则表达式时遇到的问题

标准的正则表达式是什么样的

Node.js(JavaScript)

在正则表达式中，斜杠（/）用来表示正则表达式的开始和结束。在JavaScript中，正则表达式可以使用斜杠包裹起来，以表示这是一个正则表达式的字面量。

在Node.js中，可以使用正则表达式的test()方法来检查一个字符串是否匹配某个模式。以下是一个示例代码，演示了如何使用正则表达式匹配以1开头，后面跟着两个数字的字符串：

const str = '123';
const regex = /^1\d{
    
    2}$/;

if (regex.test(str)) {
    
    
  console.log('匹配成功');
} else {
    
    
  console.log('匹配失败');
}

在上面的示例中，^1\d{2}$是一个正则表达式，它的含义是：

^：匹配字符串的开头
1：匹配字符1
\d{2}：匹配两个数字（\d表示任意数字，{2}表示匹配两次）
$：匹配字符串的结尾

因此，该正则表达式可以匹配以1开头，后面跟着两个数字的字符串。在示例中，str的值为123，它符合这个模式，所以输出结果为匹配成功。

Java

private void RegTest2() {
    
    
        String content ="abc$(abc(1.23(";
        //匹配(
        String regStr = "\\d{2}";
//        String regStr = "\\.";
        Pattern pattern = Pattern.compile(regStr);
        Matcher matcher = pattern.matcher(content);
        while (matcher.find()){
    
    
            Log.i(TAG,"match:" + matcher.group(0));
        }
    }

2023-08-11 17:49:18.021 27898-29062/cn.jj.reg I/JJWorld.MainActivity: match:23

结论

不同语言正则表达式有区别，缺乏统一的正则标准。

ASCII码表

java中合法表示字符串中转义符的方式

java读取文件assets中ini文件时，转义符消失的问题

java读取文件时，分为了三步。

第一步通过inputStream获取输入流。

如果将读取到的数据依次打印的话，可以看到是读取到了转移字符的

Properties properties = IniPropertiesReadUtils.loadFileFromAssetsNew(this, "jjapm1.ini");

     //读取Assets目录下的配置文件
    public static Properties loadFileFromAssetsNew(Context context, String filePath) {
    
    
        if (null == context || null == filePath || filePath.length() == 0)
            return null;

        InputStream assetFileIS = null;
        InputStreamReader assetFileISReader = null;
        Properties properties = new Properties();
        int readData = 0;
        try {
    
    
            assetFileIS = context.getResources().getAssets().open(filePath);
            while ((readData = assetFileIS.read())!= -1){
    
    
                Log.i(TAG,"read:" + (char)readData);
            }
        } catch (IOException e) {
    
    
            e.printStackTrace();
            properties = null;
        } finally {
    
    
            try {
    
    
                if (null != assetFileIS) {
    
    
                    assetFileIS.close();
                }
                if (null != assetFileISReader) {
    
    
                    assetFileISReader.close();
                }
            } catch (IOException e) {
    
    
                e.printStackTrace();
            }
        }
        return properties;
    }

2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:c
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:l
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:a
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:s
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:s
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:R
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:u
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:l
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:e
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read: 
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:=
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read: 
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:ä
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:¸
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:­
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:{
    
    
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:\
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:d
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:\
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:d
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:"
2023-08-12 10:05:26.258 27428-27460/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read:}

上面打印的控制信息不管，可见是打印出来了classRule = 中{\d\d"}的，只不过中文是乱码。

第二步 通过InputStreamReader获取输入字符流，处理乱码问题

//读取Assets目录下的配置文件
    public static Properties loadFileFromAssetsNew(Context context, String filePath) {
    
    
        if (null == context || null == filePath || filePath.length() == 0)
            return null;

        InputStream assetFileIS = null;
        InputStreamReader assetFileISReader = null;
        Properties properties = new Properties();
        int readData = 0;
        try {
    
    
            assetFileIS = context.getResources().getAssets().open(filePath);
//            while ((readData = assetFileIS.read())!= -1){
    
    
//                Log.i(TAG,"read:" + (char)readData);
//            }
            assetFileISReader = new InputStreamReader(assetFileIS, "UTF-8");
            while ((readData = assetFileISReader.read())!= -1){
    
    
                Log.i(TAG,"read11:" + (char)readData);
            }
        } catch (IOException e) {
    
    
            e.printStackTrace();
            properties = null;
        } finally {
    
    
            try {
    
    
                if (null != assetFileIS) {
    
    
                    assetFileIS.close();
                }
                if (null != assetFileISReader) {
    
    
                    assetFileISReader.close();
                }
            } catch (IOException e) {
    
    
                e.printStackTrace();
            }
        }
        return properties;
    }

2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11:c
2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11:l
2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11:a
2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11:s
2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11:s
2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11:R
2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11:u
2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11:l
2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11:e
2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11: 
2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11:=
2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11: 
2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11:中
2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11:{
    
    
2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11:\
2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11:d
2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11:\
2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11:d
2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11:"
2023-08-12 10:06:52.827 27565-27600/cn.jj.reg I/JJWorld.IniPropertiesReadUtils: read11:}

转义符依然是存在的，classRule = 中{\d\d"}

第三步 properties.load(assetFileISReader)对转义符进行了特殊处理，导致转义符失效

JSONObject对转义符的处理

    private void jsonRegTest() throws JSONException {
    
    
        String jsonStr = "{key:\"va\\lue\"}";
        // JSONObject对\的处理
        JSONObject jsonObject = new JSONObject(jsonStr);
        Log.i(TAG, "jsonRegTest:" + jsonObject.toString());
    }

    public JSONObject(@NonNull String json) throws JSONException {
    
    
        this(new JSONTokener(json));
    }

new JSONObject会创建一个JSONTokener。JSONTokener保留设置进来的字符串。

    public JSONTokener(String in) {
    
    
        // consume an optional byte order mark (BOM) if it exists
        if (in != null && in.startsWith("\ufeff")) {
    
    
            in = in.substring(1);
        }
        this.in = in;
    }

JSONObject(String)核心代码

    public JSONObject(@NonNull JSONTokener readFrom) throws JSONException {
    
    
        /*
         * Getting the parser to populate this could get tricky. Instead, just
         * parse to temporary JSONObject and then steal the data from that.
         */
        Object object = readFrom.nextValue();
        if (object instanceof JSONObject) {
    
    
            this.nameValuePairs = ((JSONObject) object).nameValuePairs;
        } else {
    
    
            throw JSON.typeMismatch(object, "JSONObject");
        }
    }